The present invention relates to a method for self-pierce riveting, in particular using semitubular punch rivets to connect at least two components, in particular two sheets, with the aid of a self-pierce riveter having a punch. The punch rivet to be set is pressed by the punch through the sheets to be connected.
Self-pierce or punch riveting has been known for many years, including in automobile manufacturing technology. Typically, aluminum sheets are connected with the aid of semitubular rivets at an overlap joint.
Punch riveting is understood as a riveting method in accordance with DIN 8593-5, edition September 2003, in which a solid rivet or semitubular rivet is driven by a punch through at least two non-perforated sheet-like components with the aid of a clamping device. A die is situated on the component side facing away from the punch, which forms the buttress to the clamping device, on the one hand, and is used, on the other hand, for the purpose of deforming the lower component and/or the rivet in the lower component such that a form fitting connection results between the punch rivet and the lower component. If semitubular punch rivets are used, the semitubular punch rivet does not exit from the lower component.
The punch-riveting tool suitable for this purpose typically includes a C-shaped frame, a die being provided on one side and a hydraulically or pneumatically movable punch being provided on the other side, which is enclosed by a clamping device. Punch riveters of this type are typically fastened to robots, which then move the punch riveters to the fastening point.
To set a punch rivet, it is placed in front of the punch. The clamping device then moves down and presses the two components to be connected against the die at the rivet point. Subsequently, while maintaining the clamping force of the clamping device, the punch rivet is driven into the two non-perforated components to be connected. Forces of 30 kN or more are required for this purpose. The clamping forces are in the order of magnitude of 6-7 kN.
A system of this type for a semitubular punch rivet is described in U.S. Pat. No. 5,752,305 A, for example. Clamping forces of a few hundred newtons up to 15 kN are referred to as typical here. With clamping forces at a level of this type according to the US patent, a deep-drawing procedure is to be avoided in the sheets in the area of the punch rivet, which has not proven to be correct in practice, however.
The present invention provides a method for setting punch rivets, in which a reduction of the joining forces is possible while maintaining the known punch riveters.
The present invention provides a method for setting punch rivets, in particular semitubular punch rivets, connecting at least two components, in particular two sheets, with the aid of a punch riveter having a punch. The punch rivet to be set is pressed by the punch through the sheets to be connected. The sheets to be connected are exclusively pressed together via the punch rivet to be set before the setting of the punch rivet, so that a possibly existing gap between the sheets to be connected is nearly removed, and the punch rivet is only set then.
In contrast to the prior art, a clamping device which presses together the sheets to be joined is no longer used, but rather the sheets are pressed together before the actual setting procedure via the punch and the punch rivet itself. The clamping device, which is still present, is only still used for guiding the rivet during the supply of the punch rivet to the surface of the components to be connected by the punch. However, it may no longer apply clamping force, because it no longer touches the components to be connected. Surprisingly, it has been shown that the clamping force to be applied via the rivet is less than previously used and the setting force, i.e., the force with which the punch rivet is driven into the sheets/components, may also be significantly reduced. Therefore, less tool wear arises because of the lower joining forces, and the punch rivet clamp itself may also be minimized in regard to weight and thus material costs. Therefore, even robots having a small carrying force may be used. A further advantage may be seen in that the punch riveters used up to this point may be maintained without structural changes. Only the controller of the clamping device must be altered, so that it is ensured that the clamping device no longer touches the components to be connected.
In a preferred embodiment, the method utilizes a waiting time at a constant clamping force. This waiting time may be used for determining the component thicknesses via a distance measurement of the punch path, which is known per se.
It is also known to simultaneously glue the components to be connected using punch rivets, in that adhesive is applied in spots or strips on the two interior sides of the sheets/components to be connected before the punch rivet is set. To distribute the adhesive on the sheet surfaces before the punch riveting, either longer waiting times are set at constant clamping force, or alternatively, the level of the clamping force may be changed. An advantage of this embodiment is that the air channels otherwise occurring in the adhesive distributed between the sheets when using a clamping device for clamping and thus distributing the adhesive may be significantly reduced.
In particularly preferred embodiments, ranges for the waiting time and for the clamping force when connecting two aluminum sheets of typical configuration are provided, which ranges, i.e., 0.1 to 2 seconds and 2 to 10 kN, are used in automobile manufacturing.
It is noted once again that according to the present invention, the clamping force is exclusively exerted via the punch rivet on the sheets/components to be connected and not—as in practice—via the clamping device.
In the following example, the punch riveting procedure up to this point using semitubular punch rivets is briefly described and compared to the procedure according to the present invention.
Two sheets to be connected are chucked precisely in position in a known manner. A punch riveter fastened to a robot is then moved to the connection point. The punch riveter is typically attached to a rivet stock and a rivet feed unit.
In the method according to the prior art, after a semitubular punch rivet is supplied and positioned in front of the punch head of a commercially available punch riveter, the clamping device is moved down so that it presses together the sheets to be riveted and presses them against the die situated on the component bottom side. In this way, the adhesive previously applied to the interior sides of the sheets to be connected is distributed. For this purpose, clamping forces of 2 to 10 kN are applied via the clamping device for a period of time of 0.1 to 2 seconds.
Subsequently, the punch having the pre-mounted semitubular punch rivet moves toward the sheets and penetrates the uppermost sheet, while expanding in the lowermost sheet because of the die under the lowermost sheet, without exiting from the sheet. This procedure lasts approximately 0.5 seconds. Setting forces of up to 90 kN are applied, depending on the sheet material and thickness.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.